Data for: Sediment nitrate reduction processes in response to environmental gradients along an urban river-estuary-sea continuum
Sediment dentrification (DEN), anaerobic ammonium oxidation (Anammox), and dissimilatory nitrate reduction to ammonium (DNRA) are three important nitrate (NO3–) reduction pathways in aquatic ecosystems. These processes modify nitrogen (N) loadings from land to the ocean, having important implication on management of coastal eutrophication. Here, we present rate and gene abundance data on these three pathways along a N-laden urban river-estuary-sea continuum comprised of three types of ecosystems (urban river, estuary, and adjacent sea) in the densely populated Shanghai-East China Sea area. Physiochemical data for each sampling site are also included in this dataset. We found the DEN, Anammox, and DNRA rates decreased seaward along the continuum both in summmer and winter in reponse to decreasing sediment organic matter (OM, 20 to 7 to 7 mg C g-1), ferrous oxide (Fe(II), 9 to 2.7 to 2.8 mg Fe g-1), and bottom water dissolved inorganic nitrogen (DIN, 543 to 112 to 21 μM) concentrations. Among these pathways, DEN remained the major component (~69.6%) throughout the continuum, while Anammox (47.9%) rivaled DEN (48.3%) in the urban river habitat in winter. N retention index (NIRI), ratios between retained and removed DIN, ranged from 0–0.5 and increased downstream. Annually, the continuum removes ~38.6% of N input from the Great Shanghai area. The estuary and adjacent sea removed most of the loading in absolute terms, but urban river removed more per km2, and thus was a N cycling hotspot. Together, these results suggest that the decreasing gradient of OM and inorganic matter shape the distribution of NO3– reduction along the continuum, reflecting the diminishing impact of river and human inputs from the urban river to the ocean. This data product can be used for metadata analysis to advance our understanding of nitrogen cycling and dynamics.